Recently, it has entered into a ubiquitous period where information can be approached at anytime and anywhere, and a digital convergence proceeds rapidly, in which computer, telecommunication and information are blended or fixed to electrics-electronics. As a result, the importance of the display becomes greater, which serves as an interface between electronics-information utility and human beings.
Upon reviewing the current status of development of the display, a light-weighted, thin and flat Liquid Crystal Display (LCD) that reduces eye fatigue has already been widely used instead of a large-sized and heavy Cathode-Ray Tube (CRT). Further, Organic Light Emitting Display (OLED) has also been developed, which is lighter and thinner than LCD, and can vividly display more rapid mobile images than LCD. Furthermore, a study for developing a flexible display device that is thinner, lighter and unbroken is continuing by manufacturing the display on a flexible substrate using polymer film instead of glass substrate.
A flexible display device is a flat display that is manufactured on a flexible substrate that is bendable, and since the flexible display device is foldable, bendable or deformed into a roll shape while having excellent displaying characteristics, it is evaluated as a next generation technology at a current flat plate display market and thus various studies thereon are being made globally.
A flexible display device uses basically a flat plate display that is foldable, bendable or rollable within several centimeters like paper, and thus is light in weight, thin, superior in impact-resistance and freely bondable, unlike the existing display that uses a rigid glass substrate.
The flexible display device can be prepared in the shape of a wearable display, an electronic book, an electronic paper or the like, and the application range thereof is very wide so that it can be applied to a display product of various shapes.
Here, a bending stress is applied to a display sheet of the flexible display device due to a bending force, wherein when the bending stress is intensively applied to a layer that is easily ruptured by the bending stress among the stacked structure constituting the display sheet, or the bending stress is concentrated on a bonding portion between layers, damages such as crack or peeling-off may occur on the display sheet. In this case, the basic function of the flexible display device as a display device cannot be maintained at all.